Magnetic tape and magnetic tape cartridge

ABSTRACT

A magnetic tape which is run at a speed of 4 m/sec. or higher and has recording tracks with a width of 21 μm or less, and which comprises a non-magnetic support, at least one magnetic layer formed on one surface of the non-magnetic support, and a backcoat layer formed on the other surface of the non-magnetic support, wherein servo signals for controlling tracking are recorded on the magnetic layer or the backcoat layer, characterized in that the value of (α/W)×(V/f) is 10 [s −1 ] or less, and/or the value of (α/W) is 0.1 or less, wherein V [mm/sec.] is a tape-running speed is; α [μm] is an amount of a weave with a cycle of f [mm] on one edge of the tape or the other edge thereof as the reference side for the running of the tape; and W [μm] is a width of the recording track. This magnetic tape can decrease PES and off-track and thus is excellent in servo tracking performance.

TECHNICAL FIELD

[0001] The present invention relates to a magnetic tape cartridge havinga large recording capacity, a high access speed and a high transferspeed. In particular, the present invention relates to a single reeltype magnetic tape cartridge suitable for data-backup, comprising amagnetic tape which records magnetic signals or optical signals forservo tracking, and reproduces magnetically recorded signals withreproducing heads comprising magnetoresistance elements (hereinafterreferred to as “MR head”).

BACKGROUND ART

[0002] Magnetic tapes have found various applications in audio tapes,videotapes, computer tapes, etc. In particular, in the field of magnetictapes for data-backup (or backup tapes), tapes having memory capacitiesof several tens GB or more per one reel are commercialized inassociation with increased capacities of hard discs for back-up.Therefore, it is inevitable to increase the capacity of this type oftape for data-backup. It is also necessary to increase the feeding speedof tape and a relative speed between the tape and heads in order toquicken the access speed and the transfer speed.

[0003] To increase the capacity of tape for data-backup per one reel, itis necessary to increase the length of tape per reel by decreasing thetotal thickness of the tape, to decrease the thickness demagnetizationso as to shorten the recording wavelength by forming a magnetic layerwith a thickness as very thin as 0.3 μm or less, and to increase therecording density in the tape widthwise direction by narrowing thewidths of the recording tracks to 21 μm or less, particularly 15 μm orless.

[0004] When the thickness of the magnetic layer is reduced to 0.3 μm orless, the durability of the tape tend to lower. Therefore, at least oneprimer layer is provided between a non-magnetic support and the magneticlayer. When the recording wavelength is shortened, the influence ofspacing between the magnetic layer and the magnetic heads becomesserious. Thus, if the magnetic layer has large projections or dents,which leads to a decrease in output due to spacing loss, an error rateincreases.

[0005] When the recording density in the tape-widthwise direction isincreased by narrowing the width of the tracks to 21 μm or less,particularly 15 μm or less, magnetic flux leaking from the magnetic tapeis decreased. Therefore, it is needed to use MR heads which utilizemagnetoresistance elements capable of achieving high output from verysmall magnetic fluxes, for reproducing heads.

[0006] Examples of the magnetic recording media used in combination withMR heads are disclosed in JP-A-11-238225, JP-A-2000-40217 andJP-A-2000-40218. In these magnetic recording media, skewness of outputfrom the MR heads is prevented by controlling the magnetic flux from themagnetic recording medium (a product of a residual magnetic flux densityand the thickness of the medium) to a specific value, or the thermalasperity of the MR heads is suppressed by reducing the dents orprojections on the surface of the magnetic layer to a specific value orless.

[0007] When the width of the tracks is decreased, the reproductionoutput lowers due to off-track. To avoid such a problem, track servo isneeded. As types of such track servo, there are an optical servo typeand a magnetic servo type. In either of the types, track servo isperformed on a magnetic tape drawn out from a magnetic tape cartridge(which may be also called a cassette tape) of single reel type whichhouses only one reel having the magnetic tape wound thereon in abox-like casing body. The reason for using a single reel type cartridgeis that the tape can not be stably run in a two-reel type cartridgewhich has two reels for drawing out the tape and for winding the same,when the tape-running speed is increased (for example, 2.5 m/second orhigher) so as to quicken the data transfer speed. The two-reel typecartridge has another problem in that the dimensions of the cartridgebecome larger and that the memory capacity per volume becomes smaller.

[0008] As mentioned above, there are two types of track servo systems,i.e., the magnetic servo type and the optical servo type. In the trackservo type, servo bands (200) as shown in FIG. 9 are formed on amagnetic layer by magnetic recording, and servo tracking is performed bymagnetically reading such servo bands. In the optical servo type, servobands each consisting of an array of dents is formed on a backcoat layerby laser irradiation or the like, and servo tracking is performed byoptically reading such servo bands. Other than these types, there issuch track servo in which magnetic servo signals are also recorded on amagnetized backcoat layer in the magnetic serve type. Further, as otheroptical servo type, there is such one that can record optical servosignals on a backcoat layer which is formed of a material capable ofabsorbing light or the like.

[0009] Then, the principle of the track servo system is simply describedby way of the former magnetic servo type.

[0010] As shown in FIG. 9, in the magnetic tape (3) for the magneticservo type, servo bands (200) for track serve which extend along thelengthwise direction of the tape, and data (300) for recording datathereon are formed on the magnetic layer. Each servo band (200) consistsof a plurality of servo signal-recording sections (201) on which therespective servo track numbers are magnetically recorded. A magnetichead array (not shown) which records and reproduces data on and from amagnetic tape consists of a pair of MR heads for servo track (forwardrunning and backward running), and for example, 8×2 pairs ofrecording-reproducing heads (in which the recording heads are magneticinduction type heads and the reproducing heads are MR heads). Inresponse to a signal from a MR head for servo track which has a readservo signal, the entire magnetic head array moves interlockingtherewith, so that the recording-reproducing head moves in the widthwisedirection of the tape to reach the data track (for example, eight datatracks are provided corresponding one serve track in a magnetic headarray on which 8×2 pairs of recording-reproducing heads are mounted).

[0011] In this stage, the magnetic tape runs in such a state that one ofthe tape edges extending along the lengthwise direction is regulated inits tape widthwise position by the inner surface of a flange of a guideroller provided on a magnetic recording-reproducing unit (a tape-drivingunit) (see FIG. 7). As seen in FIG. 3, the edge (3 a) of the magnetictape (3) generally has a corrugated unevenness called edge weave or edgewave. Therefore, the magnetic tape (3), even though running alongsidethe inner surface of the flange as the reference for the tape running,very slightly fluctuates in the position in the widthwise direction.However, this problem is solved by employing the above servo system:that is, even if the position of the magnetic tape very slightlyfluctuates in the widthwise direction, the entire magnetic head arraymoves in the tape widthwise direction in association with such afluctuation, so that the recording-reproducing head can always reach acorrect data track. In a system for recording tracks with widths of 24μm or more, the off-track margins are increased by widening the width ofthe recording track in comparison with the width of the reproducingtrack [for example, (the width of the recording track: about 28 μm, andthe width of the reproducing track: about 12 μm) or (the width of therecording track: about 24 μm, and the width of the reproducing track:about 12 μm)]. In such a case, there arises little decrease in thereproducing output due to off-track, even when about 3 μm of fluctuation(edge weave) in the position of the magnetic tape occurs.

[0012] However, when the width W of the record track is reduced to 21 μmor less, a decrease in output of reproduction due to off-track appearsin spite of about 3 μm of edge weave which raised no problem in theconventional record tracks. This is because, when the reproduction trackwidth should be equal to the conventional one in order to ensure areproduction output, the off-track margin becomes narrower. Further,when the recording track width is as narrow as 21 μm or less, it isconfirmed that not only the absolute value of edge weave but also thecycle of the edge weave and the tape running speed have a complicatedrelationship with respect to the off-track. To apply the servo system toa magnetic tape having record tracks with a width as narrow as 21 μm orless, a relationship among the cycle f and the amount α of edge weave,the record track width W, the tape running speed V, and the headfollowability is carefully examined. As a result, the following arerevealed: a positioning error signal (or PES, i.e. a value indicatingnon-uniformity in positional dislocation, or the value of a standarddeviation σ) becomes larger, if the values of α/W and (α/W)×(V/f) exceedspecific values, wherein α is an amount of the edge weave (in the tapewidthwise direction of the tape edge (the direction Y-Y′ on FIG. 3))with a cycle of f; V [mm/second] is a tape running speed; and W [μm] isa width of the record track. As a result, a tracking error is induced.This phenomenon raises a new problem when the width of the record trackis set at 21 μm or less.

[0013] This is described below. Since the magnetic head array as a wholehas large mass, the magnetic head array can not move following themotion of the magnetic tape in the widthwise direction, when the valuesof (α/W). and/or (α/W)×(V/f) exceed specific values, wherein a is anamount of the edge weave with a cycle of f on an edge of the tape (notonly one edge (3 a) of the tape as shown in FIG. 3, but also both edges(3 a, 3 a′) of the tape as described below) regulated in its positionwhile the tape is running; W is a width of the record track; and V is atape-running speed. As a result, a positioning error signal or PESbecomes larger. When the off-track margin is small, it is presumed thatthe off-track becomes larger. This phenomenon is not so serious when thewidth of the record track is 24 μm or more. Why this is not so seriousis that, if the motion of the magnetic head array is slow and the PES islarge, the width of the record track is sufficiently larger than thewidth of the reproducing track, so that the off-track margin is large:for example, about 6 μm or more of off-track margin is formed on eachside, when the width of the record track is about 28 μm, and the widthof the reproducing track is about 12 μm, or when the width of the recordtrack is about 24 μm, and the width of the reproducing track is about 12μm. Therefore, a decrease in the output of reproduction due to off-trackhardly occurs.

[0014] As mentioned above, in the magnetic recording-reproducing unit(i.e., the tape-driving unit), the width of the groove of the guideroller (the distance between the inner surfaces of a pair of flangesprovided on the both edges of a guide roller, see FIG. 7) is set at adimension several ten micrometers larger than the width of the magnetictape. Therefore, the cycle f and the amount α of the edge weave as thereference side for running are dominant over the linearity of a servesignal. On the other hand, in a unit for recording serve signals (aserve writer), the width of the groove of the guide roller is set at adimension substantially equal to the width of the magnetic tape so thatthere is little clearance. Therefore, both tape edges (3 a, 3 a) of thetape serve as the reference sides for tape running, and thus, the cyclef and the amount a of the edge weaves of both tape edges (3 a, 3 a) aredominant over the linearity of the servo signal. Therefore, to decreasethe off-track by decreasing PES, the relationship among the cycle f andthe amount a of the edge weaves of both tape edges (3 a, 3 a), the widthW of the record track, and the tape-running speed V should satisfy theabove equation.

[0015] When the width of the record track is as narrow as 21 μm and thelevel of PES becomes larger, an off-track error occurs, so that a normalservo control can not be preformed. Such a problem commonly arises inboth of the magnetic servo type and the optical servo type, and it ismore remarkable in the optical servo type, because the mass of theentire magnetic head array used in the optical servo type is larger thanthat used in the magnetic servo type.

DISCLOSURE OF THE INVENTION

[0016] The present invention is to overcome the foregoing problems, anda primary object of the present invention is to provide a magnetic tape,a PES from which is low and which hardly causes an off-track even whenthe width of a record track is as narrow as 21 μm or less, and amagnetic tape cartridge comprising the same.

[0017] As a result of the present inventors' intensive researches inorder to achieve the above object, they have found out that the level ofPES becomes lower, and that an off-track hardly occurs even when thewidth of a record track is as narrow as 21 μm or less, if the values ofα/W and (α/W)×(V/f) are smaller than specific values, wherein V is atape-running speed; α is an amount of edge weave with a cycle of f onone tape edge 3 a or the opposite tape edge 3 a′ served as a referenceside for the running of the tape; and W is a width of the record track.Thus, the present invention is accomplished based on such findings.

[0018] Accordingly, the present invention provides a magnetic tape and amagnetic tape cartridge as described below.

[0019] A magnetic tape according to the present invention is used at arunning speed of 4 m/sec., and it comprises a non-magnetic support, atleast one magnetic layer formed on one surface of the non-magneticsupport, and a backcoat layer formed on the other surface thereof,wherein servo signals for use in the control of tracking are recorded onthe magnetic layer or the backcoat layer, and the width of record tracksis 21 μm or less. The magnetic tape is characterized in that the valueof (α/W)×(V/f) is not larger than 10 [s⁻¹], and/or the value of α/W isnot larger than 0.1, wherein α [μm] is an amount of edge weave with acycle of f [mm] on one tape edge 3 a or the opposite tape edge 3 a′served as a reference side for the running of the tape; V is atape-running speed; and W [μm] is a width of the record track as shownin FIG. 3.

[0020] A magnetic tape cartridge according to the present inventioncomprises a box-shaped casing body (1), and one reel (2) around which amagnetic tape (3) according to the present invention is wound, arrangedin the casing body (1), and tracking control is done by servo signalsrecorded on the magnetic tape (3), while the position of one edge of thetape serving as a reference side for the tape running is being regulatedin the widthwise outward direction.

[0021] As shown in FIGS. 2 and 8, in the one-reel type magnetic tapecartridge according to the present invention, the outer circumferentialwall of the winding shaft (23) of the reel (2) is tapered so that thewinding shaft (23) has a larger diameter on the side of one of the edgesof the tape which serves as a reference side for the running of the tape(on the side of the upper end surface of the winding shaft (23) as seenin FIGS. 2 and 8). The distance between the inner surfaces of the flangeportions (21 and 22) which oppose to each other at a position justoutside the winding shaft (23) and on the inner circumference of thereel (the reel flanges having large diameters arranged adjacent to bothend faces of the winding shaft (23)) is assumed as S1, and the distancebetween the inner surfaces of the flange portions (21 and 22) whichoppose to each other at a position on the outer circumference of thereel therein is assumed as S2. Under the above assumptions, the ratio ofS1 to the upper limit P of the width of the tape (S1/P) is restrictedwithin a specified range, and the ratio of the space S2 to the upperlimit P is restricted within a specified range. By doing so, the levelof PES becomes lower, so that off-track hardly occurs, and that thedamage of the edge of the tape and winding disorder of the tape arehardly caused. In this regard, the inner circumferential portion of thereel means a portion of the reel on which the first turn of the woundmagnetic tape, that is, the innermost part of the magnetic tape islocated in the wound tape in a predetermined state, and the outercircumferential portion of the reel means the outermost circumferentialportion of the reel.

[0022] In particular, the reel (2) comprises the winding shaft (23) atthe center, and a pair of the flange portions (21 and 22) having largerdiameters, located on both end faces of the winding shaft. As shown inFIG. 8, the outer circumferential surface of the winding shaft (23) istapered at an angle of 0.01 to 0.1 degrees, so that the diameter of oneend face (23 a) of the winding shaft (23) located on the side of oneedge of the tape which serves as the reference side for the running ofthe tape can be larger than the diameter of the other end face (23 b)thereof. In addition, the ratio of the above distance S1 between theinner surfaces of the flange portions (21 and 23), to the upper limit Pof the width of the tape (S1/P) is set within a range of1.010≦(S1/P)≦1.022, while the ratio of the above distance S2 between theinner surfaces of the flange portions (21 and 23), to the upper limit Pof the width of the tape (S2/P) is set within a range of(S1/P)<(S2/P)<1.041. The above arrangement is to improve the trackingservo control: that is, by the above arrangement, one edge (3 a) of thetape can be surely fitted along the inner face of the flange (71) of theguide roller (70) (the face serving as the reference for the running ofthe tape) while the tape is running, and thereby, the slight widthwisevibration of the magnetic tape (3) is suppressed or prevented as much aspossible so that the tracking servo control can be precisely performed(see FIG. 7). The ratio of (S1/P) is set preferably within a range of1.013≦(S1/P)≦1.020, more preferably within a range of1.016≦(S1/P)≦1.018. If the ratio of (S1/P) is less than 1.010, the edgeof the tape is rubbed on the guide or the like and thus easily damaged,while, if it is more than 1.022, a winding disorder of the tape tends tooccur. The ratio of (S2/P) is set preferably within a range of 1.01(S1/P) to 1.03 (S1/P), more preferably within a range of 1.015 (S1/P) to1.025 (S1/P). If the ratio of (S2/P) is less than or equal to (S1/P),the edge of the magnetic tape is rubbed on the flange of the reel duringthe tape-winding operation or the tape-drawing operation and thus issubject to damage. This phenomenon is remarkable when the height of thewinding shaft of the reel slightly differs from the height of the grooveof the guide roller. On the other hand, when the ratio of (S2/P) is1.041 or more, a winding disorder of the tape may occur. As mentionedabove, the magnetic tape cartridge for which the taper angle β and theratios (S1/P) and (S2/P) are set within the above ranges has excellentoff-track preventive performance. Further, it is desirable that thecurvature of the magnetic tape should be 2 mm or less per 1 meter lengthof the tape in order to prevent the damage of the edge of the magnetictape and the winding disorder of the magnetic tape.

[0023] In the above arrangement, either of the magnetic servo type andthe optical servo type may be employed as the track servo controlsystem. As has already been described, in the former type, servotracking is performed by magnetically reading servo bands formed on amagnetic layer by magnetic recording. On the other hand, in the lattertype, servo tracking is performed by optically reading servo bandscomposed of an array of dents formed on a backcoat layer by laserirradiation or the like. In addition to these types, other types can beemployed: for example, in a magnetic servo control system, such amagnetic tape is used that comprises a magnetic backcoat layer on whichmagnetic servo signals are recorded, or otherwise, in an optical servocontrol system, such a magnetic tape is used that comprises a backcoatlayer formed of a material capable of absorbing light so as to recordoptical serve signals.

[0024] To achieve the high density recording, the magnetic tapecartridge of the present invention is preferably arranged such thatmagnetically recorded signals on the magnetic tape are reproduced withreproducing heads which utilize magnetoresistance elements (MR heads).Further, in case of the magnetic servo control system, it is preferablethat servo signals are also reproduced by MR heads.

BRIEF DESCRIPTION OF DRAWINGS

[0025]FIG. 1 is a perspective view of a magnetic tape cartridgeaccording to the present invention, showing a general structure thereof.

[0026]FIG. 2 is a sectional view of the magnetic tape cartridgeaccording to the present invention, showing a partly simplified internalstructure thereof.

[0027]FIG. 3 is a plan view of the magnetic tape, illustrating the edgeweave in an enlarged state.

[0028]FIG. 4 illustrates a partly simplified slitting system used forslitting a magnetic sheet in the Examples of the present invention.

[0029]FIG. 5 is a partial sectional view of a tension cut rollerarranged in the slitting system, schematically illustrating a part ofsucking portions.

[0030]FIG. 6 is a plan view of a magnetically recording-reproducing unit(a tape-driving unit), used in combination with a magnetic tapecartridge.

[0031]FIG. 7 is an enlarged side view of a part of the magneticallyrecording-reproducing unit seen from the direction of the allow A ofFIG. 6, diagrammatically illustrating the magnetic tape running along aguide roller arranged in the recording-reproducing unit.

[0032]FIG. 8 is an enlarged view of the periphery of the winding shaftof the reel of the magnetic tape cartridge shown in FIG. 2, from which apart of the reel is omitted.

[0033]FIG. 9 is a diagram of a magnetic tape in which data tracks andservo bands are alternately formed on a magnetically recording layer (amagnetic layer), illustrating an example of the track servo controlsystem used in the magnetic tape.

BEST EMBODIMENTS FOR CARRYING OUT THE INVENTION

[0034]FIG. 1 illustrates a structure of a magnetic tape cartridgeaccording to the present invention, and FIG. 2 shows the internalstructure thereof. As seen in FIG. 1, the magnetic tape cartridgecomprises a box-shaped casing body (1) obtained by bonding the upper andlower casings (1 a and 1 b) to each other, one reel (2) arranged insidethe casing body (1), and a magnetic tape (3) wound around the reel (2).A tape-drawing port (4) is opened on one side of the front wall (6) ofthe casing body (1), and the port (4) is opened or closed by a slidabledoor (5). A tape-drawing member (7) is combined to the end portion atwhich the magnetic tape (3) is drawn out in order to draw out themagnetic tape (3) wound around the reel (2) from the casing. Numeral 20in FIG. 1 refers to a door spring for forcing the door (5) to move to aclosing position.

[0035] As shown in FIG. 2, the reel (2) comprises an upper flangeportion (21), a lower flange portion (22), and a winding shaft (23)which is formed integrally with the lower flange portion (22) and whichis formed in the shape of a bottomed cylindrical body opened at theupper portion. The bottom wall (23 c) of the winding shaft (23) islocated on the inlet (1 c) of the bottom wall of the casing throughwhich a driving shaft is inserted into the casing. Gear teeth are formedon the outer periphery of the bottom wall (23 c) of the winding shaft(23), and such gear teeth are to engage with a member of a tape-drivingunit (a magnetically recording-reproducing unit). A bottom hole (23 d)is provided at the center of the bottom wall (23 c) of the winding shaft(23), and this hole (23 d) is to allow an unlocking pin (not shown) ofthe tape-driving unit to enter the casing. Further, a reel-lockingmechanism for preventing unnecessary rotation of the reel (2) isprovided in the casing body (1). Numeral 12 in FIG. 2 refers to abraking button composing this reel-locking mechanism, and numeral 17refers to a spring for forcing the braking button (12) downwardly in thedrawing.

[0036] In the present invention, a magnetic tape (3), which hasrecording tracks with a width of 21 μm or less and which is run at arate of 4 m/sec. or more, is used in the magnetic tape cartridge shownin FIGS. 1 and 2. As shown in FIG. 3, one of the edges (3 a) of themagnetic tape (3) which serves as a reference side for the running ofthe tape has an edge weave with a cycle of f [mm]. The value of(α/W)×(V/f) is set at 10 [s⁻¹] or less, and/or the value of α/W is at0.1 or less, wherein α [μm] is an amount of the edge weave with thecycle of f; W [μm] is a width of the recording track; and V [mm/sec.] isa running speed of the tape. Herein, X-X′ in FIG. 3 indicates therunning direction of the magnetic tape (3).

[0037] When the relationship among the cycle f and the amount α of theedge weave, the width W of the recording track and the tape-runningspeed V is established as above, PES becomes smaller to 0.40 μm or less,and thus excellent servo track performance in which the off-track amountis 12% or less (preferably 6% or less, more preferably 5% or less) isachieved. The value of α/W is preferably 0.07 or less, more preferably0.065, far more preferably 0.05 or less, and 0 at the best. When thevalue of α/W is 0.1 or less, PES is small and thus, a decrease inreproduction output due to off-track is small. The value of (α/W)×(V/f)is preferably 4.4 [s⁻¹] or less, more preferably 4 [s^('1)] or less, and0 at the best. When the value of (α/W)×(V/f) is 10 [s⁻¹] or less, PES issmall even if the tape-feeding speed is increased, and thus, a decreasein the reproduction output due to off-track is small. Particularly whenthe amount α of the edge weave with the cycle of f is set at the abovevalue, far excellent serve track performance is obtained even when thetape-running speed is as fast as 4 m/sec., and also when the width ofthe recording track is as narrow as 21 μm or less.

[0038] Both of tape edges (3 a and 3 a′) serve as reference sides fortape-running inside a unit for recording servo signals (a servo writer,not shown). Therefore, it is necessary to set the amounts of edge weavesof both tape edges (3 a and 3 a′) at the above value in order to recordexcellent servo signals.

[0039] The reason why the edge of a tape has a weave with a short cycle(e.g., 50 mm or less) in an amount within which off-track may occur evenwhen the tape-feeding speed is about 4 m/sec. was investigated. As aresult, it is found out that the reason therefor is a short cyclefluctuation of tension, which is caused by the motion of a magneticsheet which is being slit to provide magnetic tapes. Based on thisresult, the present inventors have improved the respective elementswhich constitute a slitting system (a system for slitting a magneticsheet into a plurality of magnetic tapes with predetermined widths).More precisely, the tension cut roller (50) and the timing belt coupling(not shown) for transmitting power to the cutter-driving section (60)arranged in such a slitting system (100) as shown in FIG. 4 areimproved, and also the mechanical vibration of the cutter-drivingsection (60) is suppressed. As a result, a magnetic tape obtained by theabove slitting has 2 μm or less of a weave with a shorter cycle f (50 mmor less) at an edge of the tape. Among the above improvement, theimprovement of the tension cut roller (50) used for controlling thetension of the magnetic sheet G is the most effective means forsuppressing the widthwise fluctuation of the tape which would be causedby the edge weave with a short cycle.

[0040] Next, the reason why the edge of a magnetic tape has a weave witha relatively long cycle (e.g., 60 to 70 mm) in an amount within whichoff-track is induced at a tape-feeding speed of about 6 m/sec. isinvestigated. The cutter-driving section (60) shown in FIG. 4 has upperand lower cutters (61 and 62) which are driven to rotate in the oppositedirections to each other. These cutters are connected with a drivingmotor (not shown) through separately provided power-transmittingdevices, and are driven to rotate by this driving motor. In this case,the power-transmitting device for transmitting the power from thedriving motor to the cutter-driving section (60) is composed of a flatbelt in combination with a rubber coupling. Then, a magnetic tapeobtained by slitting in such a system has a tape edge having a decreasedamount of edge weave with a relatively long cycle, although the cycle ofthe widthwise positional fluctuation of the tape does not change. Thiseffect is superior in this case, as compared with cases of using otherpower-transmitting devices which are composed of a timing belt incombination with a rubber coupling, a flat belt in combination with ametal coupling, and a timing belt in combination with a metal coupling,respectively. Further, a method of decreasing the amount of edge weavewith a relatively long cycle has been researched. As a result, it isfound out that the amount of edge weave can be extremely decreased bydirectly driving the cutter-driving section (60) with the motor, withoutusing any power-transmitting device. In FIG. 4, numerals 90 and 91 referto guides arranged along the feeding route of the magnetic sheet G.

[0041] Further, a method of prolonging the cycle of edge weave to, forexample, 80 mm or more within which off-track is not induced even at atape-feeding speed as fast as 8 m/sec. or more has been researched. As aresult, it is found out that, by increasing the slitting speed, thecycle f becomes longer in correspondence with the ratio of the slittingspeed, although the amount of edge weave is hardly changed.

[0042] By decreasing the sucking force of the tension cut roller from aconventional pressure of 1.33×10⁴ Pa (100 mmHg) to a lower limit of1.33×10³ Pa (10 mmHg) which is the lowest pressure for enabling thetension cut, the tape widthwise fluctuation of a tape caused by the edgeweave with a short cycle can be substantially eliminated. This method,however, has a problem in that the stable production of tapes isimpaired.

[0043] As shown in FIG. 5, the tension cut roller (50) used in the aboveslitting system has sucking portions (51) which are arranged at regularintervals along the outer circumference thereof. In the conventionalsystem, these portions are composed of a plurality of holes which arearranged at regular intervals along the axial direction of the roller(50) (a direction perpendicular to the paper plane of FIG. 5).Therefore, the magnetic sheet relatively largely flutters when themagnetic sheet is repeatedly sucked and released. As a result, thewidthwise displacement of a tape (edge weave amount α) found when thecycle of edge weave is shorter in correspondence with the cycle T1 shownin FIG. 5 becomes relatively large. To obtain a magnetic tape of thepresent invention having the foregoing edge structure, a tension cutroller in which the above sucking portions (51) are replaced with meshsucking portions formed of a mesh or a porous material is used. By doingso, the amount α of edge weave with a shorter cycle corresponding to thecycle T1 shown in FIG. 5 can be decreased as compared with conventionalones, even when the sucking force from the tension cut roller (50) isset at 1.33×10⁴ Pa (100 mmHg) and when the slitting speed is increased.In other words, a magnetic tape having a tape edge structure specifiedin the present invention [a magnetic tape in which the value of(α/W)×(V/f) and/or the value of α/W is small] can be produced.

[0044] In the meantime, a magnetically recording-reproducing unit (atape-driving unit) which records or reproduces data using such amagnetic tape is provided with guide rollers (70) as shown in FIG. 6, soas to run the magnetic tape (3), drawn out of the casing body (1) of themagnetic tape cartridge, along a predetermined route. In this drawing, ahead member (80) is arranged between a pair of guide rollers (70, 70).

[0045] As shown in the enlarged figure of FIG. 7, flanges (71 and 72)are provided at both end portions of each guide roller (70) in its axialdirection to thereby regulate the widthwise position of the magnetictape (3), and the outer circumferential portion of the roller betweeneach of the pair of flanges (71 and 72) is formed as a groove (73) whichregulates the widthwise motion of the magnetic tape (the verticaldirection on FIG. 7). The width H of this groove is usually set at adimension several ten micrometers larger than the width L of themagnetic tape (3), while the depth of the groove (73) is generally 2 to3 mm. The magnetic tape (3) is run while being regulated in thewidthwise motion by both flanges (71 and 72) which together form thegroove (73). In this case, although any reason for such a phenomenon hasbeen clarified, PES can be made smaller, when the magnetic tape (3) isallowed to run while its tape edge (3 a) which has a regulated amount ofa weave with a short cycle is being in fitting contact with the innersurface of one flange (71) (located on the upper side on FIG. 7). Sincethe width of the groove on the guide roller is set at a dimensionseveral ten micrometers larger than the width of the magnetic tape asmentioned above, the servo tracking inside the magneticallyrecording-reproducing unit is performed under the dominance of theamount of edge weave on the reference side for the tape running.However, in the servo signal-recording unit, the width of the groove ona guide roller is set at a dimension substantially equal to the width ofthe magnetic tape and thus has little clearance, and therefore, bothedges of the magnetic tape serve as reference sides for running thetape. Accordingly, the amounts of edge weaves of both tape edges aredominant over the linearity of the servo tracking. Thus, it is necessaryto regulate the amounts of the edge weaves of both tape edges below thespecific values.

[0046] In the magnetic tape cartridge of the present invention, as shownin FIG. 8, the outer circumferential surface of the winding shaft (23)is tapered at an angle of 0.01 to 0.1 degree, so that one end face ofthe winding shaft (23) on the side of the edge of the tape serving asthe reference side for the running of the tape (the upper end face inFIG. 8) can have a larger diameter than that of the other end face ofthe winding shaft (the lower end face in FIG. 8). By doing so, themagnetic tape (3) can be run along the inner surface of one flange (71)which serves as the reference side for the running of the tape insidethe magnetically recording-reproducing unit. In addition, as shown inFIG. 2, the ratio of the distance S1 between the inner surfaces of theflange portions (21 and 22) which oppose to each other at a positionjust adjacent to the outer periphery of the winding shaft (23) and onthe inner circumference of the reel, to the upper limit value P of thetape width (S1/P) is set within a range of 1.010 <(S1/P)<1.022, and theratio of the distance S2 between the inner surfaces of the flangeportions (21 and 22) which oppose to each other at a position which islocated on the outer circumference of the reel, to the upper limit valueP of the tape width (S2/P) is set within a range of (S1/P)<(S2/P)<1.041.

[0047] By doing so, PES becomes far smaller, so that excellent servetrack performance with a little amount of off-track can be achieved. Inaddition, the damage of the tape edge and the winding disorder of thetape hardly occur. In this connection, the reference side for therunning of the tape in the tape widthwise direction differs depending onthe type of the magnetically recording-reproducing unit (thetape-driving unit). In correspondence with this difference, in some ofmagnetic tape cartridges, the edges of tapes facing to the upper sidesof the casing bodies (1) serve as the reference sides, and in othermagnetic tape cartridges, the edges of magnetic tapes facing to thelower sides of the casing bodies or both edges thereof serve as thereference sides. In the magnetic tape cartridge for use in the magneticservo type magnetically recording-reproducing unit shown in FIG. 6, theedge of the tape facing to the upper side of the casing body (1) servesas the reference side for running the tape, as shown in FIGS. 1, 2 and8.

[0048] Here, examples of the dimensions of the reel (2) shown in FIGS. 1and 2, and the guide roller (70) shown in FIGS. 6 and 7 are described asbelow.

[0049] The outer diameter of the reel: about 97 mm (the diameter of theoutermost circumference of the flange portion)

[0050] The outer diameter of the winding shaft: about 42 mm (thediameter of the outermost circumference of the winding shaft)

[0051] The dimension between the outer surfaces of the upper and lowerflanges (71 and 72) of the guide roller arranged in the magneticallyrecording-reproducing unit: about 12.9 mm

[0052] The dimension between the inner surfaces of the upper and lowerflanges (71 and 72) (the width H of the groove on the guide roller):about 12.7 mm

[0053] The diameters of the upper and lower flanges (71 and 72): about12 mm

[0054] The diameter of the outer circumference of the roller locatedbetween the upper and lower flanges (71 and 72): about 18 mm

[0055] The reason why the outer circumferential surface of the windingshaft (23) is tapered so that the outer diameter of the winding shaft(23) on the side of the tape edge (3 a) serving as the reference sidefor the running of the tape can be larger is as follows:

[0056] The magnetic tape (3) can be run while the edge (3 a) of the tapewhose edge weave amount a is regulated is being in fitting contact withthe inner surface of one of the flanges (71), as the reference face forthe running of the tape, on the guide roller (70) arranged in themagnetically recording-reproducing unit. As a result, PES caused by thedislocation of the relative positions of the tape edge (3 a) and theflange (71) becomes smaller, and thereby, excellent serve trackperformance with a decreased amount of off-track can be achieved. Inthis case, the taper angle of the winding shaft (23) is preferably 0.01to 0.1 degree. If the taper angle is smaller than 0.01 degree, the aboveeffect can not be expected, while, if it is larger than 0.1 degrees, thetape edge (3 a) is excessively pressed against the inner surface of oneof the flanges (71), as the reference face for the running of the tape,on the guide roller (70), so that this tape edge portion of the tape issubject to damage.

[0057] The ratio of the distance S1 to the upper limit value P of thewidth of the tape (S1/P) is preferably set within a range of1.010≦(S1/P)≦1.022. If it is less than 1.010, the edge portion of thetape is subject to damage, while, if it is more than 1.022, windingdisorder of the tape may occur. The ratio of (S1/P) is set morepreferably within a range of 1.013≦(S1/P)≦1.020, particularly within arange of 1.016≦(S1/P)≦1.018.

[0058] The ratio of the distance S2 to the upper limit value P of thewidth of the tape is set preferably within a range of(S1/P)<(S2/P)<1.041. When the ratio of (S2/P) is smaller than or equalto the ratio of (S1/P), the edge portion of the tape is rubbed on theflange of the reel when the tape is wound around or drawn from the reel,and thus, is subject to damage. This phenomenon is remarkable when theheight of the winding shaft of the reel is slightly different from theheight of the groove on the guide roller. When the ratio of (S2/P) is1.041 or more, PES caused by the dislocation of the relative positionsof the edge of the tape and the flange as the reference face for therunning of the tape on the guide roller becomes relatively large, whenthe cycle f of the tape widthwise fluctuation is equal to thefluctuation amount. As a result, the amount of off-track tends toincrease, and winding disorder of the tape may occur. Further, the ratioof (S2/P) is set preferably within a range of 1.01 (S1/P) to 1.03(S1/P), more preferably within a range of 1.015 (S1/P) to 1.025 (S1/P).

[0059] In case of a magnetic tape cartridge housing a magnetic tape witha width of ½ inch, the distance S1 between the inner surfaces of theflange portions (21 and 22) which oppose to each other at a position onthe inner circumference of the reel is, for example, 12.860 to 12.880mm, and the distance S2 between the inner surfaces of the flangeportions (21 and 22) which oppose to each other at a position on theouter circumference of the reel is, for example, 13.140 to 13.160 mm.The inner surfaces of the flange portions (21 and 23) extend linearly orsubstantially linearly from the inside of the inner circumference of thereel to the inside of the outer circumference thereof, as seen in thesection of the reel (2) taken along the radius direction.

[0060] Generally, the magnetic tape has a curvature of about 2 mm per 1m of the tape. It is preferable for the tape not to have such acurvature. When such a curvature can not be avoided, the curvature isset at 2 mm or less, preferably 1 mm or less. By setting the curvatureat such a value, the tape can be run along the inner surface of theflange on the guide roller, as the reference face for the running of thetape, with the result that PES caused by the dislocation of the relativepositions of the tape edge and the inner surface of the flange (thereference face for the running of the tape) becomes smaller.Consequently, excellent servo tracking performance with a decreasedamount of off-track can be achieved. In this regard, it is hard toprovide a magnetic tape with a curvature of less than 0.1 mm, andgenerally, a magnetic tape has a curvature of 0.1 mm or more.

[0061] Further, PES becomes larger because of the abnormal running ofthe tape. The following are considered as the causes for the abnormalrunning: (a) unbalance between a coefficient of dynamic friction betweenthe magnetic layer of a magnetic tape and the slider (material: ALTIC(alumina/titania/carbide)) and a coefficient of dynamic friction betweenthe magnetic layer of the magnetic tape and the guide roller (material:aluminum) (since a coefficient of dynamic friction between the magneticlayer of the magnetic tape and aluminum is equal to a coefficient ofdynamic friction between the magnetic layer of the magnetic tape andSUS, the latter coefficient, of which the measuring method isestablished, is generally used in place of the former coefficient); and(b) the shape of a head for writing a servo signal is unsuitable.Particularly when the coefficient of dynamic friction between themagnetic tape and the slider (ALTIC) is high, PES becomes larger becausethe magnetic tape moves in the widthwise direction simultaneously withthe movement of the magnetic head array in the widthwise direction ofthe tape, so that the off-track amount becomes larger. Therefore, it isnecessary that the coefficient of dynamic friction between the magneticlayer of the magnetic tape and the slider (ALTIC) should be 0.35 orless, preferably 0.1 to 0.3, more preferably 0.1 to 0.25. Generally, thecoefficient of dynamic friction between the magnetic layer of themagnetic tape and SUS is 0.1 to 0.3, and that between the backcoat layerof the magnetic tape and SUS, 0.1 to 0.3. It is hard to lower thesecoefficients to less than 0.10.

[0062] A rise in PES caused by the abnormal running of the magnetic tapebecomes smaller, when the ratio of μ_(mSL) to μ_(mSUS)[(μ_(mSL))/(μ_(mSUS))] is from 0.7 to 1.3, wherein μ_(mSL) is acoefficient of dynamic friction between the magnetic layer and theslider material and μ_(mSUS) is a coefficient of dynamic frictionbetween the magnetic layer and SUS. A rise in PES caused by the abnormalrunning of the magnetic tape becomes smaller, when the ratio of[(μ_(mSL))/(μ_(BSUS))] is from 0.8 to 1.5, wherein μ_(mSUS) is ascoefficient of dynamic friction between the backcoat layer and SUS.

[0063] Hereinafter, the preferred examples of the elements useddaccording to the present invention will be explained.

[0064] <Non-magnetic support>

[0065] The thickness of the non-magnetic support is preferably 7.0 μm orless, more preferably from 2.0 to 7.0 μm. When the thickness of thenon-magnetic support is less than 2 μm, it is difficult to form a film.Furthermore, the strength of the resultant magnetic tape decreases. Whenthe thickness of the non-magnetic support exceeds 7.0 μm, the totalthickness of the magnetic tape increases so that the recording capacityper one reel decreases.

[0066] The Young's modulus E of the non-magnetic support in thelengthwise direction depends on the thickness of the support, and isusually at least 4.9 GPa (500 kg/mm²), preferably at least 5.88 GPa (600kg/mm²), more preferably at least 6.86 GPa (700 kg/mm²). When theYoung's modulus of the support is less than 5.88 GPa (600 kg/mm²), thestrength of the magnetic tape may decrease or the feeding of themagnetic tape may become unstable. When the thickness T of the supportis 5.0 μm or less, the rigidity (E.T³) decreases, so that the tapestrength lowers. Thus, the Young's modulus is preferable at least 9.8GPa (1,000 kg/mm²) The ratio of Young's modulus MD in the lengthwisedirection to Young's modulus TD in the widthwise direction (MD/TD) ofthe non-magnetic support is preferably from 10 to 1.8, more preferablyfrom 1.1 to 1.7, far preferably from 1.2 to 1.6, in the linear recordingtype as in the present invention. When this ratio is within this range,the head touch is improved.

[0067] Examples of such a non-magnetic support include a polyethylenenaphthalate film, an aromatic polyamide film, an aromatic polyimidefilm, etc.

[0068] Generally, both the magnetic layer-forming surface and thebackcoat layer-forming surface of the non-magnetic support have a centerline average surface roughness Ra of 5.0 to 10 nm. In order to decreasethe spacing loss by decreasing the average surface roughness Ra of themagnetic layer, such a non-magnetic support that has a magneticlayer-forming surface having an average surface roughness Ra of 10 to5.0 nm (Ra of the backcoat layer-forming surface is 5.0 to 10 nm) isused. The non-magnetic support of this type is called dual type, whichis constructed by laminating two types of non-magnetic supports.

[0069] <Primer layer>

[0070] The primer layer may be formed if needed. The thickness of theprimer layer is preferably from 0.3 to 3.0 μm, more preferably from 0.5to 2.1 μm. When the thickness of the primer layer is less than 0.3 μm,the durability of the magnetic recording medium may deteriorate. Whenthe thickness of the primer layer exceeds 3.0 μm, the effect to improvethe durability of the magnetic recording medium is saturated.Furthermore, in case of a magnetic tape, the total thickness of themagnetic tape increases, the length of the tape per one reel decreases,so that the recording capacity decreases.

[0071] The primer layer may contain carbon black (CB) to improve theconductivity, or non-magnetic particles to control the viscosity of apaint and the stiffness of the magnetic tape.

[0072] Examples of the non-magnetic particles to be contained in theprimer layer include titanium oxide, iron oxide, alumina, etc. Amongthem, iron oxide, or a mixture of iron oxide and alumina is preferable.

[0073] The surface roughness of the magnetic layer, which is formed onthe primer layer by a wet-on-wet method, can be reduced, when the primerlayer contains 15 to 35% by weight of carbon black having a particlesize of 10 to 100 nm, 35 to 83% by weight of non-magnetic iron oxidehaving a major axis length of 0.05 to 0.20 μm and a minor axis length of5 to 200 nm, and optionally 0 to 20% by weight of alumina having aparticle size of 10 to 100 nm, based on the total weight of theinorganic particles contained in the primer layer.

[0074] In general, the non-magnetic iron oxide has a needle shape. Whenparticulate or amorphous non-magnetic iron oxide is used, its particlesize is preferably from 5 to 200 nm.

[0075] The present invention does not exclude the addition of large sizecarbon black having a particle size of 100 nm or more, provided that thesurface smoothness is not impaired. In this case, the total amount ofthe small size carbon black CB and the large size carbon black CB ispreferably within the above range.

[0076] Examples of carbon black (CB) to be added to the primer layer areacetylene black, furnace black, thermal black, etc. Such carbon blackusually has a particle size of 5 to 200 nm, preferably 10 to 100 nm.When the particle size of carbon black is less than 10 nm, it may bedifficult to disperse the carbon black particles in the primer layersince carbon black has a structure. When the particle size of carbonblack exceeds 100 nm, the surface smoothness of the primer layerdeteriorates.

[0077] The amount of carbon black to be contained in the primer layermay depend on the particle size of carbon black, and is preferably from15 to 35% by weight. When the amount of carbon black is less than 15% byweight, the conductivity may not be sufficiently increased. When theamount of carbon black exceeds 35% by weight, the effects of theaddition of carbon black may saturate. More preferably, carbon blackhaving a particle size of 15 to 80 nm is used in an amount of 15 to 35%by weight, and particularly, carbon black having a particle size of 20to 50 nm is used in an amount of 20 to 30% by weight. When carbon blackhaving the above particle size is used in the above-defined amount, theelectrical resistance of the magnetic tape is decreased and the feedingirregularity is suppressed.

[0078] The non-magnetic iron oxide to be added to the primer layerpreferably has a major axis length of 0.05 to 0.20 μm and a minor axislength (particle diameter) of 5 to 200 nm in the case of theneedle-shape particles, or a particle size of 5 to 200 nm, morepreferably 0.05 to 150 nm, particularly preferably 0.05 to 100 nm in thecase of the particulate or amorphous shape particles. In particular, theneedle-shape iron oxide particles are preferable, since the orientationof the magnetic layer can be improved. The amount of the non-magneticiron oxide to be added to the primer layer is preferably from 35 to 83%by weight, more preferably from 40 to 80% by weight, particularly from50 to 75% by weight. When the particle size of the non-magnetic ironoxide (the minor axis length in case of the needle shape particle) isless than 5 nm, the iron oxide particles may not be uniformly dispersed.When the particle size exceeds 200 nm, the unevenness of the interfacebetween the primer layer and the magnetic layer may be worsened. Whenthe amount of the non-magnetic iron oxide is less than 35% by weight,the effect to increase the strength of the primer layer is small. Whenthe amount of the iron oxide exceeds 83% by weight, the strength of theprimer layer may rather decrease.

[0079] The primer layer may contain alumina in addition to iron oxide.The particle size of alumina is preferably from 10 to 100 nm, morepreferably from 20 to 100 nm, particularly from 30 to 100 nm. When theparticle size of alumina is less than 10 nm, the alumina particles maynot be uniformly dispersed in the primer layer. When the particle sizeof alumina exceeds 100 nm, the unevenness of the interface between theprimer layer and the magnetic layer may be worsened. The amount ofalumina to be added to the primer layer is usually from 0 to 20% byweight, preferably from 2 to 10% by weight, more preferably from 4 to 8%by weight.

[0080] <Lubricant>

[0081] A coating layer including the primer layer and the magnetic layermay contain a lubricant having a different function. Preferably, thecoefficient of dynamic friction of the magnetic tape against the guideof the feeding system or the slider of the MR head can be decreased,when the primer layer contains 0.5 to 4.0% by weight of a higher fattyacid and 0.2 to 3.0% by weight of a higher fatty acid ester, based onthe weight of the entire powder components in the primer layer. When theamount of the higher fatty acid is less than 0.5% by weight, the effectto decrease the coefficient of dynamic friction is insufficient. Whenthe amount of the higher fatty acid exceeds 4.0% by weight, the primerlayer may be plasticized and thus the toughness of the primer layer maybe lost. When the amount of the higher fatty acid ester is less than0.2% by weight, the effect to decrease the coefficient of friction isinsufficient. When the amount of the higher fatty acid ester exceeds3.0% by weight, the amount of the higher fatty acid ester which migratesto the magnetic layer may become large, so that the magnetic tape maystick to the guide or the like of the feeding system.

[0082] The coefficient of dynamic friction of the magnetic tape againstthe guide roller of the feeding system or the slider of the MR head canbe decreased, when the magnetic layer contains 0.2 to 3.0% by weight ofa fatty acid amide and 0.2 to 3.0% by weight of a higher fatty acidester, based on the weight of the ferromagnetic powder. When the amountof the fatty acid amide is less than 0.2% by weight, the coefficient ofdynamic friction between the head slider and the magnetic layer tends toincrease. When the amount of the fatty acid amide exceeds 3.0% byweight, the fatty acid amide may bleed out and causes a defect such asdropout.

[0083] As the fatty acid, higher fatty acids such as lauric acid,myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid,linoleic acid, etc. can be used. As the fatty acid ester, butylstearate, octyl stearate, amyl stearate, isooctyl stearate, octylmyristate, butoxyethyl stearate, anhydrous sorbitan monostearate,anhydrous sorbitan distearate, anhydrous sorbitan tristearate, etc. canbe used. As the fatty acid amide, the amides of palmitic acid, stearicacid and the like can be used.

[0084] The intermigration of the lubricants between the magnetic layerand the primer layer is not excluded.

[0085] The coefficient of dynamic friction between the magnetic layerand the slider of the MR head is preferably 0.35 or less, morepreferably from 0.1 to 0.3, particularly from 0.1 to 0.25. When thiscoefficient of dynamic friction exceeds 0.30, the spacing loss tends toarise due to the contamination of the slider. In addition, PES becomeslarger, and the off-track amount increases, because the magnetic tapemoves in the widthwise direction when the magnetic head array is movedin the tape widthwise direcrion. The coefficient of dynamic friction ofless than 0.10 is hardly realized.

[0086] The coefficient of dynamic friction between the magnetic layerand SUS is usually from 0.1 to 0.3, preferably from 0.10 to 0.25, morepreferably from 0.10 to 0.20. When this coefficient of dynamic frictionexceeds 0.25, the head and the guide rollers may easily be contaminated.It is difficult to decrease this coefficient of dynamic friction to lessthan 0.10.

[0087] The ratio of μ_(msL) to μ_(mSUS) [(μ_(mSL)/(μ) _(mSUS))] isusually from 0.7 to 1.3, preferably from 0.8 to 1.0. In this preferredrange, a rise in PES due to abnormality in the feeding of the magnetictape becomes smaller and also off-track becomes smaller.

[0088] <Magnetic layer>

[0089] The thickness of the magnetic layer is usually 0.3 μm or less,preferably from 0.01 to 0.20 μm, more preferably from 0.01 to 0.15 μm,particularly from 0.01 to 0.10 μm.

[0090] When the thickness of the magnetic layer is less than 0.01 μm, itis difficult to form a uniform magnetic layer. When the thickness of themagnetic layer exceeds 0.3 μm, the reproducing output may decrease dueto the thickness loss, or the product (Brδ) of the residual magneticflux density (Br) and the thickness (δ) becomes too large, so that thereproducing output tends to be skewed due to the saturation of the MRhead.

[0091] The product of the residual magnetic flux density in thelengthwise direction and the thickness of the magnetic layer ispreferably from 0.0018 to 0.06 μTm, more preferably from 0.036 to 0.050μTm. When this product is less than 0.0018 μTm, the reproducing outputwith the MR head may be low. When this product exceeds 0.06 μTm, thereproducing output with the MR head tends to be skewed. The use of amagnetic tape having such a magnetic layer is effective to shorten therecording wavelength, increase the reproducing output when signals arereproduced with the MR head, and decrease the skew in the reproducingoutput, so that, preferably, the ratio of output to noises can beincreased.

[0092] The coercive force of the magnetic layer is preferably from 120to 320 kA/m, more preferably from 140 to 320 kA/m, particularly from 160to 320 kA/m. When the coercive force of the magnetic layer is less than120 kA/m, the output is decreased by the demagnetizing fielddemagnetization, when the recording wavelength is shortened. When thecoercive force exceeds 320 kA/m, the recording with the magnetic headmay become difficult.

[0093] The center line average surface roughness Ra of the magneticlayer is preferably 3.2 nm or less, more preferably 0.5 to 3.2 nm,further preferably 0.7 to 3.2 nm, particularly preferably 0.7 to 2.9 nm.When the center line average surface roughness Ra is less than 0.5 nm,the running of the magnetic tape becomes unstable. When the center lineaverage surface roughness Ra exceeds 3.2 nm, PW 50 (the half width ofthe reproduction output) becomes larger or the output lowers, so thatthe error rate becomes higher.

[0094] As the magnetic powder to be added to the magnetic layer,ferromagnetic iron metal powder such as Fe powder, Fe—Co powder andFe—Nd—B powder, hexagonal barium ferrite powder, etc. may be used. Thecoercive force of the ferromagnetic iron metal powder and hexagonalbarium ferrite powder is preferably from 120 to 320 kA/m. The saturationmagnetization is preferably from 120 to 200 A·m²/kg (120 to 200 emu/g),more preferably from 130 to 180 A·m²/kg (130 to 180 emu/g) in case ofthe ferromagnetic iron metal powder. It is preferably from 50 to 70A·m²/kg (50 to 70 emu/g) in case of the hexagonal barium ferrite powder.The magnetic characteristics of the magnetic layer and the ferromagneticpowder are measured with a sample-vibration type fluxmeter under anexternal magnetic field of 128 MA/m (16 kOe).

[0095] An average major axis length of the needle-shape ferromagneticiron metal powder such as Fe powder and Fi-Co powder to be used in themagnetic tape of the present invention is preferably from 0.03 to 0.2μm, more preferably from 0.03 to 0.18 μm, particularly from 0.03 to 0.15μm. When the average major axis length is less than 0.03 μm, thedispersion of the powder in the paint is difficult since theagglomeration force of the magnetic powder increases. When the averagemajor axis length exceeds 0.2 μm, the coercive force decreases, or theparticle noise due to the particle size increases. For the same reason,the particle size of particulate ferromagnetic iron metal powder such asFe—Co—B powder is preferably from 5 to 200 nm, and the plate size of thehexagonal barium ferrite powder is preferably from 5 to 200 nm.

[0096] The average major axis length and the particle size are obtainedby actually measuring the particle sizes on a photograph taken with ascanning electron microscope (SEM) and averaging the measured values of100 particles.

[0097] The BET specific surface area of the ferromagnetic iron metalpowder is preferably at least 35 m²/g, more preferably at least 40 m²/g,most preferably at least 50 m²/g. The BET specific surface area of thehexagonal barium ferrite powder is preferably 1 to 100 m²/g.

[0098] A binder to be contained in the primer layer or the magneticlayer may be a combination of a polyurethane resin and at least oneresin selected from the group consisting of a vinyl chloride resin, avinyl chloride-vinyl acetate copolymer resin, a vinyl chloride-vinylalcohol copolymer resin, a vinyl chloride-vinyl acetate-vinyl alcoholcopolymer resin, a vinyl chloride-vinyl acetate-maleic anhydridecopolymer resin, a vinyl chloride-hydroxyl group-containing alkylacrylate copolymer resin, nitrocellulose (cellulose resins), and thelike. Among them, a mixture of the vinyl chloride-hydroxylgroup-containing alkyl acrylate copolymer resin and the polyurethaneresin is preferably used. Examples of the polyurethane resin includepolyesterpolyurethane, polyetherpolyurethane,polyetherpolyesterpolyurethane, polycarbonatepolyurethane,polyestrepolycarbonatepolyurethane, etc.

[0099] Preferably, a binder resin such as a urethane resin having COOH,SO₃M, OSO₂M, P═O(OM)₃, O—P═O(OM)₂ [wherein M is a hydrogen atom, analkali metal base or an amine salt], OH, NR¹R², N⁺R³R⁴R⁵ [wherein R¹ toR⁵ are each a hydrogen atom or a hydrocarbon group], or an epoxy groupas a functional group is used. The reason why such a binder is used isthat the dispersibility of the magnetic powder, etc. is improved. Whentwo or more resins are used in combination, it is preferable that thepolarities of the functional groups of the resins are the same. Inparticular, the combination of the resins both having —SO₃M groups ispreferable.

[0100] The binder is used in an amount of 7 to 50 parts by weight,preferably from 10 to 35 parts by weight, based on 100 parts by weightof the ferromagnetic powder in case of the magnetic layer, or based ontotal 100 parts by weight of carbon black and non-magnetic powder incase of the primer layer. In particular, the combination of 5 to 30parts by weight of the vinyl chloride-based resin and 2 to 20 parts byweight of the polyurethane resin is best.

[0101] It is preferable to use a thermally curable crosslinking agent,which bonds with the functional groups in the binder to crosslink thebinder. As the crosslinking agent, polyisocyanates, for example,tolylene diisocyanate, hexamethylene diisocyanate, isophoronediisocyanate; reaction products of these isocyanates with compoundshaving plural hydroxyl groups such as trimethylolpropane; condensationproducts of these isocyanates, and the like are preferably used. Thecrosslinking agent is used in an amount of 5 to 50 parts by weight,preferably 7 to 35 parts by weight, based on 100 parts of the binder.When the amount of the crosslinking agent contained in the magneticlayer is about 50% of that contained in the primer layer, for example,30 to 60% thereof, the coefficient of dynamic friction of the magneticlayer against the slider of the MR head is preferably decreased. Thereason why this range (30 to 60%) is preferable is that, when this ratiois less than 30%, the film strength of the magnetic layer may decrease,while, when this ratio exceeds 60%, the LRT treatment conditions shouldbe made severe to decrease the coefficient of dynamic friction againstthe slider, which leads to the increase of cost.

[0102] The magnetic layer may contain conventional carbon black (CB) toimprove the conductivity and the surface lubricity. As carbon black,acetylene black, furnace black, thermal black, etc. may be used. Carbonblack having a particle size of 5 to 100 nm is generally used, andcarbon black having a particle size of 10 to 100 nm is preferably used.When the particle size of carbon black is less than 5 nm, the dispersionof carbon black particles is difficult. When the particle size of carbonblack exceeds 100 nm, a large amount of carbon black should be added. Ineither case, the surface of the magnetic layer is roughened and thus theoutput may decrease.

[0103] The amount of carbon black is preferably from 0.2 to 5% byweight, more preferably from 0.5 to 4% by weight, particularly from 0.5to 3.5% by weight, and 0.5 to 3% by weight as the best, based on theweight of the ferromagnetic powder. When the amount of carbon black isless than 0.2% by weight, the effect of the addition of carbon black isinsufficient. When the amount of carbon black exceeds 5% by weight, thesurface of the magnetic layer tends to be rough.

[0104] <Backcoat layer>

[0105] To improve the tape-running rate, a conventional backcoat layerwith a thickness of from 0.2 to 0.8 μm may be used. When the thicknessof the backcoat layer is less than 0.2 μm, the effect to improve thetape-running rate is insufficient. When the thickness of the backcoatlayer exceeds 0.8 μm, the total thickness of the magnetic tapeincreases, so that the recording capacity of the tape per one reeldecreases.

[0106] The coefficient of dynamic friction between the backcoat layerand SUS is preferably from 0.10 to 0.30, more preferably from 0.10 to0.25. When this coefficient of dynamic friction is less than 0.10, themagnetic tape easily slips on the guide rollers, so that the running ofthe tape becomes unstable. When this coefficient of dynamic frictionexceeds 0.30, the guide rollers tend to be contaminated. The ratio ofμ_(mSL) to μ_(BSUS) [(μ_(mSL))/(μ_(BSUS))] is preferably from 0.8 to1.5, more preferably from 0.9 to 1.4. Outside this range, the off-trackof the magnetic tape due to the tape-meandering may be worsened.

[0107] As carbon black (CB) to be contained in the backcoat layer,acetylene black, furnace black, thermal black, etc. can be used. Ingeneral, carbon black with a small particle size and carbon black with alarge particle size are used. The particle size of small particle sizecarbon black is usually from 5 to 100 nm, preferably from 10 to 100 nm.When the particle size of small particle size carbon black is less than10 nm, the dispersion thereof is difficult. When the particle size ofsmall particle size carbon black exceeds 100 nm, a large amount ofcarbon black should be added. In either case, the surface of thebackcoat layer is roughened and thus the surface roughness of thebackcoat layer may be transferred to the magnetic layer (embossing).

[0108] When the large particle size black carbon having a particle sizeof 250 to 400 nm is used in an amount of 5 to 15% by weight of the smallparticle size carbon black, the surface of the backcoat is not roughenedand the effect to increase the tape-running rate is increased. The totalamount of the small particle size carbon black and the large particlesize carbon black is preferably from 60 to 98% by weight, morepreferably from 70 to 95% by weight, based on the weight of inorganicpowders in the backcoat layer. The center line average surface roughnessRa of the backcoat layer is preferably from 3 to 15 nm, more preferablyfrom 4 to 10 nm.

[0109] To increase the strength of the backcoat layer, it is preferableto add iron oxide and alumina both having a particle size of 0.1 to 0.6μm, preferably 0.2 to 0.5 μm to the backcoat layer. The amount of theiron oxide and the alumina is preferably from 2 to 40% by weight, morepreferably from 5 to 30% by weight, based on the weight of the inorganicpowder in the backcoat layer.

[0110] The binder to be contained in the backcoat layer may be the samebinders as those used in the magnetic layer and the primer layer. Amongthese binders, the combination of the cellulose resin and thepolyurethane resin is preferably used so as to decrease the coefficientof friction and to improve the tape-running rate.

[0111] The amount of the binder in the backcoat layer is usually from 40to 150 parts by weight, preferably from 50 to 120 parts by weight, morepreferably from 60 to 110 parts by weight, particularly from 70 to 110parts by weight, based on the total 100 parts by weight of the carbonblack and the inorganic powder in the backcoat layer. When the amount ofthe binder is less than 50 parts by weight, the strength of the backcoatlayer is insufficient. When the amount of the binder exceeds 120 partsby weight, the coefficient of friction may become too large. Preferably,30 to 70 parts by weight of the cellulose resin and 20 to 50 parts byweight of the polyurethane resin are used. To cure the binder, acrosslinking agent such as a polyisocyanate compound is preferably used.

[0112] The crosslinking agent to be contained in the backcoat layer maybe the same as those used in the magnetic layer and the primer layer.The amount of the crosslinking agent is usually from 10 to 50 parts byweight, preferably from 10 to 35 parts by weight, more preferably from10 to 30 parts by weight, based on 100 parts by weight of the binder.When the amount of the crosslinking agent is less than 10 parts byweight, the film strength of the backcoat layer tends to decrease. Whenthe amount of the crosslinking agent exceeds 35 parts by weight, thecoefficient of dynamic friction of the backcoat layer against SUSincreases.

[0113] The special-purpose backcoat layer, on which magnetic servosignals are recorded, may contain 30 to 60 parts by weight of theferromagnetic powder which is used in the magnetic layer, 40 to 70 partsby weight of carbon black to be used in the backcoat layer, andoptionally 2 to 15 parts by weight of the iron oxide and/or alumina tobe used in the backcoat layer. As the binder, the resin to be used inthe backcoat layer is used in an amount of usually 40 to 150 parts byweight, preferably 50 to 100 parts by weight, based on total 100 partsby weight of the ferromagnetic powder, the carbon black and thenon-magnetic inorganic powder. As the crosslinking agent, thecrosslinking agent described above is used usually in an amount of 10 to50 parts by weight per 100 parts by weight of the binder. For the samereason as described with regard to the magnetic layer, preferably, thecoercive force is from 120 to 320 kA/m, and the product of the residualmagnetic flux density Br and the thickness is from 0.018 to 0.06 μTm.

[0114] <LRT (lapping/rotary/tissue) treatment>

[0115] The magnetic layer is subjected to a LRT treatment comprising alapping, rotary and tissue treatments, so as to optimize the surfacesmoothness, the coefficient of dynamic friction against the slider ofthe MR head and the cylinder material, the surface roughness and thesurface shape. Thereby, the running rate of the magnetic tape and thereproducing output with the MR head are improved, and the spacing lossis reduced.

[0116] (1) Lapping:

[0117] An abrasive tape (lapping tape) is moved by the rotary roll at aconstant rate (standard: 14.4 cm/min.) in a direction opposite to thetape-feeding direction (standard: 400 m/min.), and is brought intocontact with the magnetic layer of the magnetic tape while being pressedunder the guide block. In this step, the magnetic layer is polishedwhile the unwinding tension of the magnetic tape and the tension of thelapping tape being maintained constant (standard: 100 g and 250 g,respectively). The abrasive tape (lapping tape) used in this step may bean abrasive tape (lapping tape) with fine abrasive particles such asM20000, WA10000 or K10000. It is possible to use an abrasive wheel(lapping wheel) in place of or in combination with the abrasive tape(lapping tape). When frequent replacement is necessary, the abrasivetape (lapping tape) alone is used.

[0118] (2) Rotary treatment

[0119] A rotary wheel having air-bleeding grooves (standard: width 1inch (25.4 mm); diameter 60 mm; width of air-bleeding grooves 2 mm;angle of groove 45 degrees, manufactured by KYOWA SEIKO Co., Ltd.) isrotated at a constant revolution rate (usually 200 to 3,000 rpm;standard: 1,100 rpm) in a direction opposite to the feeding direction ofthe magnetic layer, and allowed to be in contact with the magnetic layerof the magnetic tape at a constant contact angle (standard: 90 degrees).Thus, the surface of the magnetic layer is treated.

[0120] (3) Tissue treatment

[0121] Tissue (a non-woven fabric, for example, Traysee manufactured byToray) is fed at a constant rate (standard: 14.0 mm/min.) by rotarybars, in a direction opposite to the feeding direction of the magnetictape, while the rotary rods being pressed against the surface of thebackcoat layer and the surface of the magnetic layer of the magnetictape, respectively to clean the surfaces.

EXAMPLES

[0122] The present invention will be explained in detail by way of thefollowing Examples, which do not limit the scope of the invention in anyway. In Examples and Comparative Examples, “parts” are “parts byweight”, unless otherwise specified.

Example 1

[0123] <Components of a paint for undercoat layer> (1) Iron oxide powder(particle size: 0.11 × 0.02 μm) 68 parts α-Alumina (particle size: 0.07μm) 8 parts Carbon black (particle size: 25 nm; 24 parts oil absorption:55 g/cc) Stearic acid 2.0 parts Vinyl chloride-hydroxypropyl acrylatecopolymer 8.8 parts (—SO₃Na group content: 0.7 × 10⁻⁴ eq./g)Polyesterpoyurethane resin 4.4 parts (Tg: 40° C., —SO₃Na group content:1 × 10⁻⁴ eq./g) Cyclohexanone 25 parts Methyl ethyl ketone 40 partsToluene 10 parts (2) Butyl stearate 1 part Cyclohexanone 70 parts Methylethyl ketone 50 parts Toluene 20 parts (3) Polyisocyanate 4.4 parts(Colonate L manufactured by Nippon Polyurethane) Cyclohexanone 10 partsMethyl ethyl ketone 15 parts Toluene 10 parts <Components of a paint formagnetic layer> (1) Ferromagnetic iron metal powder 100 parts (Co/Fe: 20atomic %, Y/(Fe + Co): 3 atomic %, Al/(Fe + Co): 5 wt. %, Ca/Fe: 0 wt.%; σs: 155 A · m²/kg, Hc: 149.6 kA/in, pH: 9.4, major axis length: 0.10μm) Vinyl chloride-hydroxypropyl acrylate copolymer 12.3 parts (—SO₃Nagroup content: 0.7 × 10⁻⁴ eq./g) Polyesterpoyurethane resin 5.5 parts(—SO₃Na group content: 1 × 10⁻⁴ eq./g) α-Alumina (particle size: 0.12μm) 8 parts α-Alumina (particle size: 0.07 μm) 2 parts Carbon black(particle size: 75 nm; 1.0 part DBP oil absorption: 72 cc/100 g) Metalacid phosphate 2 parts Palmitic acid ainide 1.5 parts n-Butyl stearate1.0 part Tetrahydrofuran 65 parts Methyl ethyl ketone 245 parts Toluene85 parts (2) Polyisocyanate 2.0 parts Cyclohexanone 167 parts

[0124] A paint for primer layer was prepared by kneading the componentsof Group (1) with a kneader, adding the components of Group (2) to themixture, and stirring them, dispersing the mixed components with a sandmill in a residence time of 60 minutes, and adding the components ofGroup (3), followed by stirring and filtering the mixture.

[0125] Separately, a magnetic paint was prepared by kneading thecomponents of Group (1) with a kneader, dispersing the mixture with asand mill in a residence time of 45 minutes, and adding the componentsof Group (2), followed by stirring and filtering the mixture.

[0126] The paint for primer layer was applied on a non-magnetic supportmade of a polyethylene naphthalate film (thickness of 6.2 μm, MD=6.08GPa, MD/TD=1.3; manufactured by TEIJIN) so that the primer layer couldhave a thickness of 1.8 μm after dried and calendered, and then, thepaint for magnetic layer was applied on the primer layer by a wet-on-wetmethod so that the magnetic layer could have a thickness of 0.15 μmafter the magnetic paint layer had been oriented in a magnetic field,dried and calendered. After orientation in the magnetic field, the layerwas dried with a drier to obtain a magnetic sheet. The orientation inthe magnetic field was carried out by arranging N—N opposed magnets (5kG) in front of the drier, and arranging two pairs of N—N opposedmagnets (5 kG) at an interval of 50 cm at a position 75 cm before thefinger-touch layer-drying position in the drier. The coating rate was100 m/min. <Components of a paint for backcoat layer> Carbon black(particle size: 25 nm) 80 parts Carbon black (particle size: 370 nm) 10parts Iron oxide (major axis length: 0.4 μm; 10 parts acicular ratio:about 10) Nitrocellulose 45 parts Polyurethane resin (containing SO₃Nagroups) 30 parts Cyclohexanone 260 parts Toluene 260 parts Methyl ethylketone 525 parts

[0127] The components of a paint for backcoat layer were dispersed witha sand mill in a residence time of 45 minutes and a polyisocyanate (15parts) was added to the mixture to obtain a paint for backcoat layer.After filtration, the paint was coated on a surface of the magneticsheet opposite to the magnetic layer so that the backcoat layer couldhave a thickness of 0.5 μm after dried and calendered, and then, thebackcoat layer was dried to finish the magnetic sheet.

[0128] The magnetic sheet obtained was planished by seven-stagecalendering using metal rolls at a temperature of 100° C. under a linearpressure of 150 kg/cm, and wound around a core and aged at 70° C. for 72hours.

[0129] <Slitting Treatment>

[0130] Next, the slitting system (100) shown in FIG. 4 was used to slitthe magnetic sheet G into a plurality of magnetic tapes (3) with a widthof ½ inch. FIG. 5 is an enlarged view of the sucking section of thetension cut roller (50) shown in FIG. 4. The sucking section comprisessucking portions (51) which are communicated with a suction source (notshown) to suck the magnetic sheet, and tape-contacting portions (52)which contact the magnetic sheet at their outer peripheries. The suckingportions (51) and the tape-contacting portions (52) are arrangedalternately and at regular intervals along the outer circumferentialsurface of the tension cut roller (50). As seen in FIG. 5, the distancein the circumferential direction from the rear end of one suckingportion (51) to the rear end of the next sucking portion (51), in otherwords, the cycle TI of the sucking portions (51) is 13.5 mm. The suckingportions (51) are packed with a porous metal material to provide meshsucking portions. The slitting system (100) equipped with the abovetension cut roller (50) was used to slit the magnetic sheet G under theconditions of a sucking pressure of 1.33×10⁴ Pa (100 mmHg) and a windingangle of 188 degrees at which the magnetic sheet G was wound around thetension cut roller (50). Although not shown herein, thepower-transmitting unit for transmitting the power from the drivingmotor to the cutter-driving member (60) shown in FIG. 4 employed a flatbelt as the driving belt, and a rubber coupling as the coupling so as toabsorb the vibrations from the driving motor. Then, a LRT treatment iscarried out under the following conditions.

[0131] <LRT (lapping/rotary/tissue) treatment>

[0132] (1) Lapping

[0133] An abrasive tape (lapping tape) was fed by a rotary roll at arate of 14.4 cm/min. in a direction opposite to the feeding direction ofthe magnetic tape (400 m/min.), and was pressed down from above by aguide roller to be brought into contact with the magnetic layer of themagnetic tape. In this step, the magnetic layer was polished while theunwinding tension of the magnetic tape being maintained at 100 g and thetension of the lapping tape, at 250 g.

[0134] (2) Rotary aluminum wheel treatment

[0135] An aluminum rotary wheel having air-bleeding grooves with a widthof 2 mm (the angle of groove 45 degrees, manufactured by KYOWA SEIKOCo., Ltd.;), which had a width of 25.4 mm and a diameter of 60 mm, wasrotated at a revolution rate of 1,100 rpm in a direction opposite to thefeeding direction of the magnetic tape and brought into contact with themagnetic layer of the magnetic tape at a contact angle of 90 degrees.Thus, the surface of the magnetic layer was treated.

[0136] (3) Tissue treatment

[0137] The tissue (a non-woven fabric: Toraysee manufactured by Toray)was fed at a rate of 14.0 mm/min. in a direction opposite to the feedingdirection of the magnetic tape by a rotary bar to clean the surface ofthe magnetic tape.

[0138] Magnetic servo signals were written on the magnetic layer of themagnetic tape at a rate of 4 m/sec. (4,000 mm/sec.), using a servowriter, and this magnetic tape was wound around a reel and set in acasing body. Thus, a magnetic tape cartridge for use in a computer shownin FIGS. 1 and 2 was constructed.

[0139] The reel used in this cartridge included a winding shaft whoseouter circumferential surface was tapered at an angle of 0.03 degrees(taper angle: β) so that the diameter of the upper end face thereof onthe side of the edge of the tape as the reference side for the runningof the tape could be larger. The distance S1 between the inner surfacesof the flange portions at a position on the inner circumference of thereel therein was 12.93 mm; the ratio (S1/P) of S1 to the upper limitvalue P of the width of the magnetic tape which was 12.656 mm was 1.022;the distance S2 between the inner surfaces of the flange portions at aposition on the outer circumference of the reel therein was 13.16 mm;and the ratio of (S2/P) was 1.040 which was larger than 1.020 (S1/P).

Examples 2 to 13

[0140] Magnetic tape cartridges for computers of Examples 2 to 13 wereconstructed in the same manner as in Example 1, except that a part ofthe conditions were changed to the conditions indicated in Tables 2 or3. The term, “direct drive” as seen below means the motor's directdriving of the cutter-driving section without using anypower-transmitting device using a belt, in order to prevent theoccurrence of edge weave due to the vibration of the drive belt.

Comparative Examples 1 to 5

[0141] Magnetic tape cartridges for computers of Comparative Examples 1to 5 were constructed in the same manner as in Example 1, except thatthe slitting conditions were changed to the conditions indicated inTable 4. In these Comparative Examples, a conventional sucking sectionhaving sucking holes, but not the mesh sucking section, was used as thesucking section (51).

Examples 14 to 17

[0142] Magnetic tape cartridges for computers of Examples 14 to 17 wereconstructed in the same manner as in Example 1, except that the reelsshown in Table 5 were used.

Examples 18 to 23 and Comparative Examples 6 to 13

[0143] Magnetic tape cartridges for computers of Examples 18 to 23 andComparative Examples 6 to 13 were constructed in the same manner as inExample 1, except that the reels shown in Tables 6 to 8, and themagnetic tape of Example 3 were used. These magnetic tape cartridgeswere used for evaluating the damages of the edges of the tapes and thewinding disorder of the tapes.

[0144] The characteristics of the magnetic tape cartridges wereevaluated as follows.

[0145] <Amount of Edge Weave and Cycle thereof in the LengthwiseDirection of Tape>

[0146] The amount of a weave on the edge of a tape as the reference sidefor the tape running was continuously measured over a length of 50 m ofthe tape, with an edge weave meter (Keyence) mounted on the servowriter. The obtained amount of edge weave was subjected to Fourieranalysis to find the amount of the edge weave and the cycle of the edgeweave in the lengthwise direction of the tape.

[0147] <PES and Amount of Off-Track>

[0148] PES and the amount of off-track were determined from afluctuation in reproduction output when signals are recorded (with arecording wavelength of 0.37 μm) and reproduced, using a modified LTOdrive (the recording track width: 20.6 μm, and the reproducing trackwidth: 12 μm).

[0149] <Evaluation of Damage of Edge of Magnetic Tape and WindingDisorder of Tape>

[0150] The damage of the edge of a tape and the winding disorder of thetape were evaluated using ten LTO drives. One hundred magnetic tapecartridges in which magnetic tapes were wound around specified reelswere used for evaluation. Reference data were previously recorded on thedata regions of the magnetic tape cartridges used for evaluation, andthe data were reproduced to determine the amounts of off-track. Then,each of these cartridges was run forward and backward (reciprocated) ata rate of 4 m/sec., and this reciprocated running was repeated 1,000times. The damage of the edge of each magnetic tape after subjected tothe running test was evaluated by measuring the amount of off-trackfound after the running test. If this amount of off-track was increasedby 50% or more of the amount of off-track which had been found beforethe running test, it was evaluated that such a magnetic tape was damagedat its edge. The winding disorder of the magnetic tape after the runningtest was evaluated by visually observing the condition of the winding ofthe magnetic tape from both sides of the reel to evaluate the degree ofthe winding disorder.

[0151] <Surface roughness, median of unevenness and projection amount ofmagnetic layer>

[0152] The measurement was carried out by a scanning type white-lightinterference method with a scanning length of 5 μm using ageneral-purpose three-dimensional surface structure analyzer (New Veiw5000 manufactured by ZYGO). The field of view was 350 μm×260 μm.

[0153] (P1−P0), (P1−P20) and [(P1−P0)/Ra] were calculated, wherein Ra isa centerline average surface roughness of the magnetic layer; P₀ is acentral value of the unevenness of the magnetic layer; and P₁ is themaximum projection (the highest), and P₂, P₃, P₄; P₅ . . . P₁₉, P₂₀ arethe second highest, the third highest, the fourth highest, the fifthhighest, . . . the nineteenth highest, the twentieth highest in themagnetic layer, respectively.

[0154] <Coefficients of dynamic friction between the magnetic layer andeach of the slider material and SUS>

[0155] Against SUS:

[0156] Around a SUS pin (SUS 304) having an outer diameter of 5 mm, amagnetic tape was wound at an angle of 90 degrees under a load of 0.64N. The same part of the tape was slid at a rate of 20 mm/sec. ten times,and then a coefficient of friction was measured.

[0157] Against slider material:

[0158] Around an AlTIC pin having an outer diameter of 7 mm, a magnetictape was wound at an angle of 90 degrees under a load of 0.64 N. Thesame part of the tape was slid at a rate of 20 mm/sec. ten times, andthen a coefficient of dynamic friction was measured.

[0159] The results are shown in Tables 1 to 4. The notations in theTables mean the following.

[0160] μ_(mSL): a coefficient of dynamic friction between a magneticlayer and a slider material.

[0161] μ_(mSUS): a coefficient of dynamic friction between a magneticlayer and SUS.

[0162] μ_(BSUS): a coefficient of dynamic friction between a backcoatlayer and SUS.

[0163] Brδ: a product of a residual magnetic flux density (Br) and athickness of a magnetic layer (δ).

[0164] Hc: a coercive force of a magnetic layer. Surface roughness Ra ofa magnetic layer: a centerline average surface roughness Ra of amagnetic layer. TABLE 1 Thickness of 0.15 magnetic layer (μm) Brδ (μTm)0.045 Hc (kA/m) 155 Thickness of 1.8 primer coat layer (μm) Non-magneticsupport material/ PEN/6.2 Thickness (μm) Thickness of 0.5 backcoat layer(μm) Total thickness (μm) 8.65 Surface roughness Ra of 3.1 magneticlayer (nm) (P₁-P₀) (nm) 27.7 (P₁-P₂₀) (nm) 3.0 μ_(mSUS) 0.20[(μ_(mSL))/(μ_(mSUS))] 1.1 [(μ_(mSL))/(μ_(BSUS))] 1.2 [(P₁-P₀)/Ra] 8.9

[0165] TABLE 2 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Sucking portionMesh Mesh Mesh Mesh Mesh Mesh Mesh Sucking pressure (× 10³ Pa) 13.3 13.313.3 13.3 13.3 13.3 13.3 Winding angle 188° 188° 188° 188° 188° 188°188° Driving belt Flat Flat Flat — Flat Flat Flat belt belt belt beltbelt belt Coupling member Rubber Rubber Vibration- — Rubber Vibration-Vibration- proof proof proof rubber rubber rubber Direct drive — — —Used — — — Slitting speed (m/min.) 200 200 200 200 300 300 400 Cycle f(mm) 65 65 65 65 98 98 130 Edge weave amount α (μm) 1.5 1.5 1.3 0.8 1.51.3 1.3 Recording track width W (μm) 20.5 20.5 20.5 20.5 20.5 20.5 20.5Reproducing track width (μm) 12 12 12 12 12 12 12 Tape-feeding speed V(mm/sec.) 4000 8000 4000 4000 4000 4000 4000 α/W 0.073 0.073 0.063 0.0390.073 0.063 0.063 V/f (s⁻¹) 62 123 62 62 41 41 31 (α/W) (V/f) 4.5 9.03.9 2.4 3.0 2.6 2.0 α X (V/f) (mm/sec.) 92 185 80 49 61 53 40 PES (μm)0.15 0.30 0.13 0.08 0.10 0.09 0.07 Off-track (%) 5.5 10.9 4.7 2.9 3.63.1 2.4

[0166] TABLE 3 Ex. 8 Ex. 9 Ex. 10 Ex. 11 Ex. 12 Ex. 13 Sucking portionMesh Mesh Mesh Mesh Mesh Mesh Sucking pressure (× 10³ Pa) 13.3 13.3 13.313.3 13.3 13.3 Winding angle 188° 188° 188° 188° 188° 188° Driving belt— — — — — — Coupling member — — — — — — Direct drive Used Used Used UsedUsed Used Slitting speed (m/min.) 200 300 400 400 400 400 Cycle f (mm)65 98 130 130 130 1300 Edge weave amount α (μm) 0.8 0.8 0.8 0.8 0.8 0.8Recording track width W (μm) 20.5 20.5 20.5 20.5 20.5 20.5 Reproducingtrack width (μm) 12 12 12 12 12 12 Tape-feeding speed V (mm/sec.) 40004000 4000 6000 8000 10000 α/W 0.039 0.039 0.039 0.039 0.039 0.039 V/f(s⁻¹) 62 41 31 46 62 77 (α/W) (V/f) 2.4 1.6 1.2 1.8 2.4 3.0 α X (V/f)(mm/sec.) 49 33 25 37 49 62 PES (μm) 0.08 0.05 0.04 0.06 0.08 0.10Off-track (%) 2.9 1.9 1.5 2.2 2.9 3.6

[0167] TABLE 4 C. Ex. 1 C. Ex. 2 C. Ex. 3 C. Ex. 4 C. Ex. 5 Suckingportion 13.5 mm 13.5 mm 13.5 mm 13.5 mm 13.5 mm pitch pitch pitch pitchpitch Sucking pressure (× 10³ Pa) 1.33 1.33 1.33 1.33 1.33 Winding angle188° 188° 188° 188° 188° Driving belt Timing Flat Timing Timing Timingbelt belt belt belt belt Coupling material Rubber Rubber Metal MetalMetal Direct drive — — — — — Slitting speed (m/min.) 200 200 200 200 200Cycle f (mm) 13.5 13.5 13.5 13.5 13.5 Edge weave amount α (μm) 2.6 2.5 33 3 Recording track width W (μm) 20.5 20.5 20.5 20.5 20.5 Reproducingtrack width (μm) 12 12 12 12 12 Tape-feeding speed V (mm/sec.) 4000 40004000 6000 8000 α/W 0.127 0.122 0.146 0.146 0.146 V/f (s⁻¹) 296 296 296444 593 (α/W) (V/f) 37.6 36.1 43.4 65.0 86.7 α X (V/f) (mm/sec.) 770 741889 1333 1778 PES (μm) 0.50 0.45 0.55 1.2 1.7 Off-track (%) 24 24 27 4053

[0168] TABLE 5 Ex. 14 Ex. 15 Ex. 16 Ex. 17 Taper of winding shaft 0 0.030.01 0.1 Distance S1 at inner side of 12.97 12.87 12.78 12.93 windingshaft (mm) Ratio of S1 to upper limit P 1.025 1.017 1.01 1.022 of tapewidth (S1/P) Distance S2 at outer side of 13.29 13.15 13.05 13.16winding shaft (mm) Ratio of S2 to upper limit P 1.05 1.039 1.031 1.04 oftape width (S2/P) (S2/P) (S1/P) 1.025 1.022 1.021 1.018 PES (μm) 0.20.13 0.15 0.16 Off-track (%) 11.0 2.1 5.5 5.8

[0169] TABLE 6 Ex. 6 Ex. 18 Ex. 19 C. Ex. 7 C. Ex. 8 Taper of windingshaft 0 0.01 0.1 0.12 0.15 Distance S1 at inner side 12.87 12.87 12.8712.87 12.87 of winding shaft (mm) Ratio of S1 to upper limit 1.017 1.0171.017 1.017 1.017 P of tape width (S1/P) Interval S2 at outer side 13.1513.15 13.15 13.15 13.15 of winding shaft (mm) Ratio of S2 to upper limit1.039 1.039 1.039 1.039 1.039 P of tape width (S2/P) (S2/P) (S1/P) 1.0221.022 1.022 1.022 1.022 Damage of tape edge A A A B C Disorder inwinding of B A A A B tape

[0170] TABLE 7 C. Ex. C. Ex. C. Ex. 9 10 Ex. 20 Ex. 21 11 Taper ofwinding shaft 0.03 0.03 0.03 0.03 0.03 Interval S1 at inner side 12.7212.76 12.78 12.93 12.97 of winding shaft (mm) Ratio of S1 to upper limit1.005 1.008 1.010 1.022 1.025 P of tape width (S1/P) Interval S2 atouter side 12.94 12.97 13.00 13.15 13.19 of winding shaft (mm) Ratio ofS2 to upper limit 1.022 1.025 1.027 1.039 1.042 P of tape width (S2/P)(S2/P) (S1/P) 1.017 1.017 1.017 1.017 1.017 Damage of tape edge C B A AA Disorder in winding of A A A A B tape

[0171] TABLE 8 C. Ex. C. Ex. 12 Ex. 22 Ex. 23 13 Taper of winding shaft0.03 0.03 0.03 0.03 Interval S1 at inner side of 12.78 12.78 12.78 12.78winding shaft (mm) Ratio of S1 to upper limit P 1.010 1.010 1.010 1.010of tape width (S1/P) Interval S2 at outer side of 12.78 12.91 13.1713.31 winding shaft (mm) Ratio of S2 to upper limit P 1.010 1.020 1.0401.051 of tape width (S2/P) (S2/P) (S1/p) 1.000 1.010 1.030 1.041 Damageof tape edge C A A A Disorder in winding of tape A A A B

[0172] As is understood from the above results, the magnetic tapes whichsatisfy the following conditions make it possible to decrease PES andthe amount of off-track and thereby to provide excellent servo trackingperformance. That is, each of such magnetic tapes is used at a runningspeed of 4 m/sec. or higher, and the magnetic tape comprises anon-magnetic support, at least one magnetic layer formed on one surfaceof the non-magnetic support, and a backcoat layer formed on the otherside thereof, wherein servo signals for controlling tracking arerecorded on the magnetic layer or the backcoat layer, and wherein themagnetic tape has recording tracks with a width of 21 μm or less,characterized in that the value of (α/W)×(V/f) is 10 [s⁻¹] or less, andthe value of (α/W) is 0.1 or less, wherein V [mm/sec.] is a tape-runningspeed; α [μm] is an amount of edge weave with a cycle of f [mm] on oneedge 3 a or the other edge 3 a′ of the tape as the reference side forthe running of the tape; and W [μm] is a width of the recording track.

[0173] Further, a magnetic tape cartridge including such a magnetic tapehouses a reel which comprises a winding shaft and flange portions,characterized in that the outer circumferential surface of the windingshaft is tapered at a taper angle of 0.01 to 0.1 degrees so that one endface of the winding shaft on the side of one edge of the tape as thereference side for the running of the tape can have a larger diameter,and that the ratio of S1 to P is set within a range of1.010>(S1/P)>1.022, and the ratio of S2 to P, within a range of(S1/P)<(S2/P)<1.041, wherein S1 [mm] is a distance between the innersurfaces of the flange portions which oppose to each other at a positionjust outside the winding shaft and on the inner circumference of thereel; S2 [mm] is a distance between the inner surfaces of the flangeportions which oppose to each other at a position on the outercircumference of the reel; and P is an upper limit value of the width ofthe tape. This magnetic tape cartridge is far excellent in servetracking performance, and the damage of the edge tape and the windingdisorder of the tape are lessened.

EFFECT OF THE INVENTION

[0174] According to the present invention, a magnetic tape whichdecreases PES and off-track and thus is excellent in servo trackingperformance, and a magnetic tape cartridge including such a magnetictape are provided. The magnetic tape cartridge of the present inventionhas a larger capacity per reel, a smaller PW50 and a higher reproducingoutput, which results in a lower error rate. Thus, the magnetic tapecartridge of the present invention is suitably and highly reliably used,for example, as a backup tape for computers.

1. A magnetic tape comprising a non-magnetic support, at least onemagnetic layer formed on one surface of the non-magnetic support, and abackcoat layer formed on the other surface of the non-magnetic support,wherein servo signals for controlling tracking are recorded on themagnetic layer or the backcoat layer, said magnetic tape havingrecording tracks with a width of 21 μm or less and being run at a speedof 4 m/sec. or higher, characterized in that the value of (α/W)×(V/f) is10 [s⁻¹] or less, wherein is V [mm/sec.] is a tape-running speed; α [μm]is an amount of a weave with a cycle of f [mm] on one edge of the tapeor the other edge thereof as the reference side for the running of thetape; and W [μm] is a width of the recording track.
 2. A magnetic tapecomprising a non-magnetic support, at least one magnetic layer formed onone surface of the non-magnetic support, and a backcoat layer formed onthe other surface of the non-magnetic support, wherein servo signals forcontrolling tracking are recorded on the magnetic layer or the backcoatlayer, said magnetic tape having recording tracks with a width of 21 μmor less and being run at a speed of 4 m/sec. or higher, characterized inthat the value of (α/W) is 0.1 or less, wherein V [mm/sec.] is atape-running speed; α [μm] is an amount of a weave with a cycle of f[mm] on one edge of the tape or the other edge thereof as the referenceside for the running of the tape; and W [μm] is a width of the recordingtrack.
 3. A magnetic tape comprising a non-magnetic support, at leastone magnetic layer formed on one surface of the non-magnetic support,and a backcoat layer formed on the other surface of the non-magneticsupport, wherein servo signals for controlling tracking are recorded onthe magnetic layer or the backcoat layer, said magnetic tape havingrecording tracks with a width of 21 μm or less and being run at a speedof 4 m/sec. or higher, characterized in that the value of (α/W) is 0.1or less, and that the value of (α/W)×(V/f) is 10 [s⁻¹] or less, whereinV [mm/sec.] is a tape-running speed; α [μm] is an amount of a weave witha cycle of f [mm] on one edge of the tape or the other edge thereof asthe reference side for the running of the tape; and W [μm] is a width ofthe recording track.
 4. A magnetic tape cartridge comprising abox-shaped casing body, and one reel around which a magnetic tapeclaimed in claim 1, 2 or 3 is wound, arranged in the casing body,wherein the tracking of the magnetic tape cartridge is controlled byservo signals recorded on the magnetic tape.
 5. A magnetic tapecartridge comprising a box-shaped casing body, and one reel around whicha magnetic tape is wound, arranged in the casing body, wherein thetracking of the magnetic tape cartridge is controlled by servo signalsrecorded on the magnetic tape, characterized in that the reel comprisesa winding shaft at the center, and flange portions arranged on both endfaces of the winding shaft; that the outer circumferential surface ofthe winding shaft is tapered at a taper angle of 0.01 to 0.1 degrees sothat one end face of the winding shaft on the side of one edge of thetape as the reference side for the running of the tape can have a largerdiameter than the other end face thereof; and that the ratio of S1 to Pis set within a range of 1.010≦(S1/P)≦1.022, and the ratio of S2 to P,within a range of (S1/P)<(S2/P)<1.041, wherein S1 [mm] is a distancebetween the inner surfaces of the flange portions which oppose to eachother at a position on the inner circumference of the reel is; S2 [mm]is a distance between the inner surfaces of the flange portions whichoppose to each other at a position on the outer circumference of thereel; and P [mm] is an upper limit value of the width of the tape.
 6. Amagnetic tape cartridge according to claim 5, wherein one reel aroundwhich a magnetic tape claimed in claim 1, 2 or 3 is wound is arranged inthe box-shaped casing body.
 7. A magnetic tape cartridge according toany one of claims 4 to 6, wherein the servo signals are recorded asmagnetic signals on the magnetic layer or the backcoat layer of themagnetic tape.
 8. A magnetic tape cartridge according to any one ofclaims 4 to 6, wherein the servo signals are recorded as optical signalson the backcoat layer of the magnetic tape.
 9. A magnetic tape cartridgeaccording to any one of is claims 4 to 8, wherein magnetically recordedsignals on the magnetic tape are reproduced by a reproducing head whichutilizes a magnetoresistance element.
 10. A magnetic tape cartridgeaccording to any one of claims 4 to 9, wherein the curvature of themagnetic tape is 2 mm or less per 1 meter length of the tape.